Safety and arming mechanism



April 23, 1957 e. ROVE ETAL SAFETY AND ARMING MECHANISM 3 Sheets-Sheet J.

Filed Feb. 18, 1953 EE 5 M. G

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INVENTORS GENE ROVE aid/fidu- .9. a m nronnsvs;

GEORGE S. VAN DYKE JR. BENJAMIN D. NABRESKI April 23, 1957 e. ROVE ETAL 2,789,508

SAFETY AND ARMING MECHANISM Filed Feb. 18, 1953 3 Sheets-Sheet 3 INVENTORS. SES'EES EAN DYKE JR ar NJAMIN'D. NABRESKII United States Patent SAFETY AND G MECHANISM Gene Rove and George S. Van Dyke, Jr., Philadelphia, Pa., and Benjamin D. Nabreski, Haddon Heights, N. J., assignors to the United States of America as represented by the Secretary of the Army Application February 18, 1953, Serial No. 337,698 6 Claims. (Cl. 102-83) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured by or for the Government for governmental purposes without the payment of any royalty thereon.

The present invention relates to fuzes for missiles and more particularly to an improved safety and arming mechanism useful with such fuzes.

2 fuze which will provide greater safety both during handling and firing over prior art mechanisms of like kind.

Another object of the present invention is to provide a safety mechanism for missile fuzes which will guard against arming of the fuze until the missile is subjected to a predetermined inertial force.

Still another object of the present invention is to provide a safety mechanism for missile fuzes which will guard against arming of the fuze until the missile is subjected to a predetermined inertial force which is sustained for a minimum time interval.

An additional object of the present invention is to provide a safety and arming device for missiles which is actuated only under sustained acceleration.

A further object of the present invention is to provide a timing mechanism for controlling delayed arming of a in which the detonator is exploded by passing an electric current through a high resistance circuit to generate a heat and detonate the primer charge. In the latter case, the current source may comprise any source of electrical energy such, for example, as an electrical condenser discharge circuit, a battery having a high amperage, or other suitable electrical source.

In any case, it is obvious that safety measures need be provided to prevent premature firing during handling and shipping of the missile, as well as to offset the hazards incident at short range once the missile is fired. In addition thereto, in the case of long range missiles in which a booster is employed to launch the missile, if there should be a failure of the booster or other circumstance which would cause abrupt termination of the trajectory in the vicinity of the launcher, safety conditions dictate that the detonator be disabled. These requirements can be met by providing the missile with a safety and arming mechanism which, regardless of circumstances, prevents the primer or first charge in the explosive train from being detonated except upon certain factors being present. In

other words, the missile is rendered safe until it is intended to be armed and ready to detonate.

Most safety and arming devices heretofore provided have been made responsive either to an inertial or centrifugal force, or to a mechanical, spring controlled, timing arrangement. The devices which are dependent upon an inertial force utilize a mass or weighted body which operates mechanically either in response to setback as the missile accelerates upon being fired or in response to setforward which occurs upon impact or sudden deceleration fuze and also for controlling arming after a sustained inertial force.

It is also an object of the present invention to provide a safety and arming mechanism which is relatively simple in construction and highly efiicient in use. I i

In accordance with the present invention, the safety and arming device comprises a clockwork arrangement for moving an electrical detonator between safe and armed positions. The clockwork arrangement consists of two escapement mechanisms arranged to operate successively. Operation of the first escapement mechanism in the series is effected by an inertial force resulting from propulsion of the article it is used with. Upon completion of operation of the first escapement mechanism, that is, after a sustained minimum acceleration has set back the mass sufliciently, the device is arranged to disconnect or unlock the escapement mechanism of the second clockwork mechanism for effecting rotation of the detonator to an armed, ready-tofire position. The second escapement mechanism is arranged to operate under the influence of spring control for a predetermined time interval. If the minimum acceleration required to operate the first clockwork mechanism is not maintained for the required minimum, the mechanism is arranged to interrupt movement of the detonator to its armed position and thereby guard against premature firing. If, however, circumstances warrant no interruption in arming the device once the required acceleration has been sustained for the required minimum time, a second embodiment of the present in: vention provides for locking the first clockwork mechanism against interrupting operation of the second clockwork mechanism.

The novel features of the present invention, as well as additional objects and advantages thereof, will be understood better from the following detailed description of a preferred embodiment of the invention when read in connection with the accompanying drawings in whichi Fig. l is a front elevation of a safety and arming device in accordance with one embodiment of the present invention, the parts being shown in a locked, safe position pre paratory to arming, and with a portion of a cover plate being broken away to show certain construction details; Fig. 2 is a view, similar to Fig. 1, showing thesamei parts unlocked and after movement of the detonator to an armed position; Fig. 3 is a fragmentary side elevation of the device shown in Fig. l;

Fig. 4 is a rear elevation of the device shown in Fig. 1 portions thereof being broken away and another cover plate removed to shown certain details of construction;

Fig. 5 is a sectional view of the rotor and rotor housing, taken along the line 5-5 of Fig. 3, the electricalcom-act v being shown disposed in shunt, the position they are'di'sposed in while the detonator is in a safe position;

Fig. 6 is a sectional view, similar to Fig. 5, but showingand arming device in accordance with a second embodiment of the present invention;

Fig. 1s a sectional view of a portion of the apparatus shown in Fig. 9, the view being taken along the line 1010 of Fig. 9 and showing a locking feature with the parts disposed in an unlocked position; and

Fig. 11 is a view, similar to Fig. 10, showing the looking feature with the parts disposed in a locked position.

Referring more particularly to the drawings, wherein similar reference characters are used to. designate corresponding parts throughout, two preferred embodiments of the present invention are shown.

The first embodiment, which is illustrated in Figs. 1 through 8 of the drawings, comprises a safety and arming device 1 useful with a missile fuze (not shown) to prevent premature arming of the fuse until after the missile has been launched from the weapon it is used with. The safety and arming device 1 is of a design, size and construction which is suitable to the particular fuze it is intended to be used with and comprises, generally, a frame or suitable support 3, anelectric detonator 5, and two clockwork mechanisms 7, 9.

The frame 3 is made from any suitable material and, as herein shown, comprises a base 11 and a wall or plate 13 supported on the base and arranged to extend normal to the base. The electric detonator 5 is disposed within a rotor assembly mounted on one side of the plate 13 and located remotely from the base 11. One of the clockwork mechanisms 7 is mounted on the side of the plate 13 opposite to the rotor assembly 15. The other clockwork mechanism 9 is mounted on the same side of the plate 13 as the rotor assembly and between the rotor assembly and the base.

The rotor assembly 15 comprises a rectangular prism 17, preferably of a light-weight, insulating material, a metal cylindrical rotor housing 19 and a cylindrical rotor 21 of insulating material. A central aperture 23 is provided in the prism 17 for receiving the rotor housing 19, the aperture extending through the prism. The prism is;mounted onthe wall plate 13 with the axis of the aperture disposed normal to the .plate, or, in other words, parallel to the base 11. The rotor housing 19 comprises a cup-shaped member which is securely fastened within the prism aperture 23 by screws or bolts 24 and the rotor 21 is mounted within the housing for rotation about its ,own axis. The rotor 21 is provided with a transverse bore 25 extending diametrically therethrough. The transverse bore is of stepped construction to provide a shoulder or stop 27 for the electrical detonator 5. The large diameter portion of the transverse bore is threaded to facilitate mounting and securing the detonator within the rotor.

The detonator 5 is used in the explosive train of the missile to initiate by flame action a powder train (not shown), such as Primacord currently in use. The powder train, in turn, ignites the explosive charge of the missile. The detonator 5 comprises a suitable electronic type which operates in response to passage of an electric current-through a high resistance circuit thereby to generate a heat sufiicient to ignite the primer mixture containcd therein. As herein shown, the detonator is somewhat cylindrical in shape and has one end 29 thereof threaded complementary tothe threaded bore of the rotor. The opposite end 30 of the detonator is of smaller diameter than the threaded end 29 and contains the primer mixture. Two wires 31, 33 extend from the. primer mixture end 30 centrally through .thewthreaded end. 29 and areof a length suitable. to provide. connections to electrical contacts carried by the rotor. An annular recess 35 is provided in the cylindrical outer surface of the rotor 21 within which the detonator connections 31, 33 are disposed thereby to facilitate making connections with resilient contact members 37, 39 mounted at spaced intervals within th recess. The contact members are made long enough to extend beyond the outer cylindrical periphery of the rotor and are arranged to bear against the inner cylindrical periphery of the rotor housing. Thus, the contact members are arranged in wiping contact with the electricaily conductive rotor housing. Obviously, as long as both members are in'contact with the rotor housing they will be in shunt and prevent ignition of the primer mixture by an electrical charge.

Suitable electrical conductors 41, 43 are provided on the rectangular prism 17 for convenience in effecting a connection with an external electrical source. As shown particularly in Fig. 4 of the drawings, one of these conductors 41 is mounted on the outside surface of the prism and is attached to-the metal rotor housing 19 by one of the housing fastening bolts 24. Thus, the rotor housing functions as one terminal of the electrical circuit. The other conductor 43 is in threaded engagement with and extends through the body of the prism and an insulator 47 provided within a cut-away portion of the cylindrical wall of the rotor housing. The insulator 47 is of a size and is arranged to extend across the path of the resilient contact members 3'7, 39 upon rotation of the rotor in the housing. The end 49 of the conductor which extends through the insulator is located within the path of the conductors and functions as the other terminal of the electrical circuit.

Thus, with the terminals, that is, the rotor housing 19 and the conductor 43, and the resilient contact members 37, 39 arranged in the manner aforesaid, upon rotation of the rotor to the armed position shown in Fig. 6 of the drawings, the one contact member 37 is in contact with the conductor terminal 43 and the other contact member 39 is in contact with the rotor housing. In this position, the contact members will no longer be in shunt but will connect the detonator in circuit with the electrical source preparatory to receiving an electrical impulse for initiating detonation of the primer mixture. The arrangement functions as a switch for the detonator and thereby provides an additional safety device to prevent the detonator from being fired accidentally by a premature or accidental electrical impulse.

in addition to its function as a safety switch, the rotor and rotor housing operate to effect another safety'feature. As shown particularly in Fig. 7 of the drawings, when the rotor is in a position such that the resilient contact members are in shunt, the-detonator 5 is disposed out of alignment with an opening 51 provided in the rotor housing 19 and another opening 53 aligned therewith and which extends through a wall of the prism 17. The prism'opening 53 is provided for accommodating one end of a Primacord therein upon assembly of the safety and arming mechanism in the missile fuze; Thus, when the rotor is revolved in the housing to the position in which the resilient contact members 37, 39 are in circuit with the electrical energy. source, the position indicated in Fig. 6 of the drawings, the detonator will likewise have been moved to a position in alignment with the openings 51, 53 so that it will= be directly exposed to the Primacord'. In this position, the mechanism is said to be armed and ready for firing. Although'the angle of rotation of the rotor between the; safe and armed positions herein illustrated is approximately degrees, this angle is, not controlling and may differ according to the particular requirements.

Rotation of the rotor and detonator 5 is produced by a mechanical clockwork mechanism -7 mounted opposite to the rotor assembly 15. This clockwork mechanism 7 comprises a gear train journaled, betweenthe assemblyv wall 13 andaplatc 55. The, plate 5.5. is mounted in space'drelation to the wall 13 by suitable pillars 57 and bolts 59. The gear train 7 is driven by a coil spring 61 the inner end of which is anchored to an arbor 63 and the outer end of which is attached to an adjacent pillar. Fixed to the arbor 63 is a gear 65 which drives an escapement wheel 67 through a pinion and gear train 69. Continuous move ment of the escapement wheel 67 is checked intermittently by a pallet wheel 71 of conventional type. The pallet wheel 71 comprises a body portion or, mass 75 mounted for pivotal movement about an axis 77 and two pins 73 extending from the body portion. The lower portion of the pallet wheel body 75, that is, the portion disposed on the opposite side of the axis from the pins 73, is bifurcated to provide a slot 79 for locking purposes. The arbor 63 is of a length to extend through the assembly wall 13 as well as the adjacent prism wall and is connected with the rotor 21 in a manner to effect rotation of the rotor between safe and armed positions in response to operation of the clockwork mechanism. A stop 81 is provided which the arbor gear 65 engages to stop the mechanism in a position which .will insure alignment of the detonator with the openings 51, 53 providing access to the Primacord. I

The spring operated clockwork mechanism 7 is arranged to function as a timing mechanism in effecting a time delay upon movement of the detonator between safe and armed positions. A further time delay, as well as an additional safety device, is provided by the other clockwork mechanism 9 which is located beneath the rotor assembly 15.

This other clockwork mechanism 9 comprises a gear train which is similar to the spring operated clockwork mechanism '7 except that it is inertia operated. The gear train of the inertia operated mechanism is journaled between the assembly wall 13 and another plate (not shown). The other plate is also mounted in spaced relation to the wall 13 by suitable pillars 85 and bolts 87. The gear train 9 includes a rack 89 and pinion 91 assembly for driving an escapement wheel 93. Movement of the escapement wheel is checked intermittently by a pallet wheel 95 similar to the first mentioned pallet wheel 71. The rack 89 comprises a mass or body which partially surrounds the assembly wall 13 and is arranged for slidable movement along the assembly wall between a position adjacent to the spring operated mechanism 7 and a position adjacent to the base 11. A locking detent 97 is mounted on the upper end of the rack body 89 and arranged to extend into the slot 79 of. the bifurcated body portion 75 when the rack body is positioned adjacent to the spring operated mechanism 7, that is, in the manner shown particularly in Fig. 1 of the drawings. Thus, when the locking detent 97 and the rack body 89 are interengaged or coupled together, the spring operated mechanism 7 is locked against movement. A spiral spring 99 is provided both for normally biasing the rack body into a locked position and for retarding or opposing the force of inertia acting upon the rack body upon firing the missile. The mass of the rack body 89 and the amount of bias applied by the spring will, of course, be determined according to the particular requirements of timing and set back.

In accordance with the aforesaid arrangement, the safety and arming mechanism of the present invention will be found to operate as follows. With the detonator mounted in the rotor 21, the rotor is disposed in a safe position preparatory to arming, in the manner indicated in Figs. 1, 4, 5 and 7 of the drawings. In this position, the inertia operated mechanism 9 is set with the locking detent 97 engaged with the pallet wheel body 75 thereby to prevent operation of the spring operated mechanism 7 and movement of the detonator to the armed position. The safety and arming device is then prepared and ready for assembly in the fuze with the base of the mechanism arranged for orientation rearwardly in the missile with respect to the other components of the safety and arming mechanism thereby to effect proper operation of the inertia operated mechanism upon firing the missile.

Immediately upon firing no action takes placein the safety and arming mechanism. Not until a prescribed minimum inertia force has been developed is the rack body 89caused to be set back or moved backward against the resistive force of the spiral spring 99. Movement of the rack body rearwardly is thereby not only delayed or retarded by the spiral spring but also by the clockwork mechanism connected therewith. After a predetermined time interval, as determined by the length of time it requires to move the locking detent 97 as amount suflicient to withdraw it from the slot 79 of the pallet wheel 71, the spring operated mechanism 7 is released for operation. As long as the required inertia force is maintained, the spring mechanism will rotate the rotor 21 and move the detonator 5 from the safe position to the armed position. In the armed position, the detonator is not only aligned with the passages 51, 53 leading to the Primacord" but it is also connected electrically in circuit with the source of electrical power necessary for detonation.

From the foregoing description, it will be recognized that the safety and arming device of the present invention provides additional safety measures over those of prior art arrangements of like kind by utilizing a combination of two independently operative clockwork mechanisms to effect rotation of the detonator from a safe to an armed position. Not only is safety obtained by the conventional system of utilizing a spring operated clockwork mechanism to produce a time delay but, in addition thereto, there must be a sustained minimum inertial force for a pre-' determined length of time before the apparatus will arm the fuze. Obviously, should the inertial force be not great enough, for example, in the case where, in handling, the missile is dropped, the spring operated mechanism will not be unlocked and the appartus will not operate to fire the missile. In other words, the present invention affords safety in handling in a way which is unobtainable in other set back types of arrangements. On the other hand, if the inertial force is not sustained for a minimum period of time, the rack body 89 will be moved forwardly by the spiral spring 99 and cause the locking detent 97 to engage the pallet wheel 71 and check further rotation of the detonator. In addition to these measures, an adequate time delay is provided first by the retarded action of the inertia operated mechanism 9 until it releases the spring operated mechanism 7 and next by the retarded action of the spring mechanism until it rotates the detonator to the armed position.

In the event that circumstances warrant no interruption in arming the fuze once the missile is fired, a second embodiment of the present invention includes a locking arrangement 101 which is provided on the mass or rack body 89. The locking arrangement shown in Figs. 9 through 11 of the drawing comprises at least one locking detent 103 disposed in a recess 105 provided in the rack body. A coil spring 107 is compressed between the detent and a bolt 109 which threadedly engages the rack body and is disposed in the recess for retention of the detent. The end 111 of the detent oppositely disposed from the end engaged by the spring 107 is seated within an aperture 113 extending through the wall of the rack body adjacent to the assembly wall. The assembly wall is cut away to receive the detent end 111 when the rack body is set back an amount sufiicient to release the lock ing detent from the spring mechanism pallet wheel. With this arrangement, once the rack body is set back sufficiently to initiate operation of the spring mechanism, the spring mechanism will not be interrupted in its operation of rotating the detonator to an armed position regardless of a reduction in speed of travel of the missile.

It will be observed from the foregoing description that the present invention provides a safety and arming mechanism which insures not only safety in handling but also in flight and guards against premature firing by depending upon a combination of sustained set back forces and timing devices before it is armed and ready to fire.

In addition thereto, it will also be recognized that the present invention serves to prevent premature arming of the fu'ze until after the missile has left the weapon.

' It will become apparent to those persons skilled in the art that the apparatus is not only simple in construc tion but positive in operation. Although but two modifications of the present invention are shown and described herein, it will undoubtedly become apparent to those skilled in the art that many other forms or modifications thereof are possible within the spirit of the invention. For example, the arrangement of gears may be changed, the mass of the rack body may difier, or the angle of travel of the rotor between safe and armed positions may be altered to satisfy particular requirements. On the other hand, the rack and gear mechanism may be oriented to be responsive to centrifugal forces rather than set back forces. Therefore, it is desired that the present invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

We claim:

1. An acceleration actuated arming mechanism comprising: detonator support means mounted for rotation about an axis between two positions angularly related to each other; rotating means comprising a time delay mechanism operatively associated with said support means; and control means for initiating operation of said time delay mechanism, said control means being detacha'bly connected with said rotating means and being so constructed and arranged for detachment from said rotating means in response to propulsion of the arming mechanism, said control means including a rack and pinion, the rack comprising a mass mounted for movernent in response to an inertial force produced as the result of propulsion of the arming mechanism, said control means also including means in engagement with the rack for preventing movement of that rack until a sustained minimum inertial force acts upon the rack.

2. The invention as defined in claim 1 wherein said rack includes locking means for holding said rack in a detachedposition, said locking means being responsive only to movement of said control means to a position disengaged from said time delay mechanism.

3. An acceleration actuated arming mechanism for use in detonating an explosive charge, such mechanism comprising: an electric responsive detonator; means supporting said detonator for'movement between a first position apart from communication with the explosive charge and 8 a second position in direct communication with the explosive'charge; means carried by said support means adapted for connection with a source of electrical energy, said electrical connecting means being disposed to provide a Shunt connection for said detonator when said su port means is located in the first position and to eliminate the shunt connection and connect said detonator in circuit with the source of electrical energy only in the second position of said detonator; and time delay means connected with said support means for moving said detonator between the first and second positions, said time delay means comprising two mechanical units having separate motive power means, those units being connected for successive operation, one of the units being responsive to detachment from the other one of the units.

4. The invention as defined in claim 3 wherein a first one of said units comprises a spring driven gear train connected with said detonator support means for movement thereof between said two positions, a second one of said units comprising an inertia driven rack and gear mechanism, said rack including means detachably connected with said first unit for preventing operation of said first unit while connected therewith, operation of said first unit being initiated in response to detachment of said rack means from said first unit.

5. The invention as defined in claim 4 wherein said second unit includes means connected therewith and operative to effect release of said first unit only upon a sustained minimum acceleration of said arming mechanism.

6. The invention as defined in claim 5 wherein said second unit includes means disposed to engage said first unit to interrupt operation of said first unit in response to deceleration of said arming mechanism below said minimum acceleration.

References Cited in the file of this patent UNITED STATES PATENTS 1,142,375 Smith June 8, 1915 1,665,666 Junghans Apr. 10, 1928 1,726,325 Varaud Aug. 27, 1929 2,086,527 Aughey July 13, 1937 2,369,310 McGrath et a1 Feb. 13, 1945 2,486,362 OBrien Oct. 25,1949

FOREIGN PATENTS 328,410 Germany Nov. 5, 1920 

